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roca (Mechanical) (OP)
3 Oct 07 3:39
I am reviewing 2 tubesheet designs for a TEMA Type N channel.
The Channel and Shell ID are 1740mm
Design Pressure Tubeside / Shellside = 90 barg / 22 barg
Design Temperature = 100°C / 85°C
Corrosion Allowance = 0 mm
3709 seamless tubes – 19.05 mm OD x 1.6 mm wall
Pitch = Triangular, 23.812 mm pitch
Straight tube length 15650 mm
Unsupported tubespan 706 mm

Tubesheet, tubes, channel and shell materials = Duplex (S31803)

One design is done to TEMA 8th edition using the PV Elite 2006 software and the required tubesheet thickness = 172 mm

The other design is done to ASME VIII Div 1 UHX using the PV Elite 2006 software and the required tubesheet thickness = 285 mm

Why the big difference….?

Which one do you believe – I would say TEMA as it has been around for longer..?

I have been advised that UHX has still got several errors in it…….?
LSThill (Mechanical)
3 Oct 07 9:15
roca (Mechanical)

Did you buy PVElite/CodeCalc 2007-QA Manual from CODE?

The PVElite/CodeCalc Verification and Quality Assurance Manaul provide users with a standard set of PVElite/CodeCalc job used in the verifying both the operation of the program and the accuracy of the result for each release of the PVElite/CodeCalc package.

L S THILL

eliebl (Mechanical)
3 Oct 07 9:28
Sorry that I do not know what type "N" refers to but I have experinced tubesheets where the stresses in the adjacent shell or channel have caused minimum tubesheet thickness to double.  This is may be a case where the strength of the tubesheet is not a concern but the tubesheet thickness has been increased to keep the junction from becoming overstressed.

Have you read the white papers detailing the background of UHX?  They are not a bad read and give a better understanding of what UHX is trying to accomplish.  I am not aware of any obvious errors in UHX but I do know that there are many scenarios which UHX cannot be applied to due to some of the assumptions pointed out in the white paper.  Rigid unperforated ring around the outside being one.

Regards,
EJL
vesselguy (Petroleum)
3 Oct 07 13:15
roca,

I have not done any tube sheet cals for a long time, but I do know that UHX is the mandatory tube sheet thickness cal if you want your exchanger to be U-stamped.  TEMA is only applicable for every other parts of the exchanger mechanical design except for tubesheet thickness.   Eliebl can confirm what I'm saying.   Don't get me wrong but I think questioning which thickness is right is mute because you have to meet code.  You can write to Section VIII committe to challenge them later though...

Just ma 2cents.

SnTMan (Mechanical)
3 Oct 07 18:13
roca, did you run the "elastic-plastic" calculation in UHX?
This calculation allows for (under certain circumstances) increased stresses in the adjacent integral cylinder and can sometimes result in a thinner tubesheet than otherwise. Study this in Part UHX and your software manuals. I believe
this is the effect eliebl refers to.

Sometimes, no matter what, Part UHX is going to give a thicker tubesheet, as TEMA was condsidered "non-conservative" for some conditions.

The whitepaper is a good read.

These days, I calculate tubesheets per TEMA and Part UHX and use the thicker.

Regards,

Mike
Helpful Member!  TomBarsh (Structural)
3 Oct 07 18:19
UHX accounts for the rotational support of the tubesheet edges by the shell (ie: bending is shared by the shell). In some cases this will cause UHX to require greater tubesheet thickness than would TEMA. UHX allows for use of thicker shell section ("shell bands") adjacent to the tubesheet. Try specifying shell bands to reduce the required thickness of the tubesheet.

gr2vessels (Mechanical)
3 Oct 07 22:57
Hi roca,
If you design for use in WA, you'll be probably better off with AS 3857, which is more accurate than TEMA and UHX put together. You also could ring Peter McGowen in Melbourne, at Orica head office, for the latest updates on the standard.
cheers,
gr2vessels
roca (Mechanical) (OP)
4 Oct 07 20:43
Thanks Guys
Helpful Member!  Mandeep1 (Mechanical)
8 Oct 07 12:40
Roca,

In the output of the UHX you will find a parameter, XA. Which is tube bundle stiffness / shell stiffness. If
 
Xa < 3        => ASME gives thicker tubesheet
3 < Xa < 9 => ASME is closer to TEMA
Xa > 9        => ASME gives thinner tubesheet.

check the Xa parameter in your case. The TEMA standard does not account for the stresses at the junction of the tubesheet and the shell/channel, while UHX does. Some good suggestions have been provided earlier in this discussion.

Here is one link to the UHX white paper, it explains the differences between the TEMA and ASME in detail.

http://www.coade.com/support_reference.asp?vartype=13&varflag=PVElite

gr2vessels, is there any comparison between UHX, TEMA with the AS 3857 code.

Thanks,
Mandeep

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